1. Technical Field
The present invention relates to an optical position detection device for optically detecting the position of a target object, and a hand device and a display device with a position detection function each provided with the optical position detection device.
2. Related Art
As the optical position detection device for optically detecting the position of the target object, there is proposed, for example, a device (see, e.g., JP-T-2003-534554 (Document 1; the term “JP-T” as used herein means a published Japanese translation of a PCT patent application)) of emitting detection light beams respectively from two light beam sources toward the target object via a transmissive member, and then receiving the component of the detection light beams, which are reflected by the target object and transmitted through the transmissive member, by a common light detector.
In the configuration described in Document 1 described above, the position of the target object is detected based on the ratio between the emission intensities of the detection light beams when controlling the two light beam sources so that the receiving intensity of the light detector in the case in which the detection light beam emitted from one of the two light beam sources is reflected by the target object and the receiving intensity of the light detector in the case in which the detection light beam emitted from the other of the two light beam sources is reflected by the target object become equal to each other.
In the configuration described in Document 1, since the method of using the spatial relationship between the detection light beams emitted from the two light beam sources is adopted, it is required to accurately control the emission intensities of the detection light beams from the light beam sources. In order for achieving the above, although it is required to set the emission intensity of the light beam sources while monitoring inspection light beams emitted from the two light beam sources in the condition without the target object, Document 1 fails to propose the configuration therefor.
Further, in the configuration described in Document 1, some of the detection light beam emitted from each of the two light beam sources is reflected by a surface of the transmissive member on the side opposite to the side where the target object is located, and is received by the light detector. Therefore, the reception intensity in the light detector is a result of combining the reception intensity of the detection light beam reflected by the target object and the reception intensity of the light beam other than the detection light beam reflected by the target object. Therefore, there arises a problem that the position detection accuracy is degraded if the position of the target object is detected based on the ratio between the emission intensities of the detection light beams when controlling the two light beam sources so that the receiving intensity of the light detector in the case in which the detection light beam emitted from one light beam source is reflected by the target object and the receiving intensity of the light detector in the case in which the detection light beam emitted from the other light beam source is reflected by the target object become equal to each other.